Many distinct genetic abnormalities occur in cancer and are often linked to specific regions of the genome as evidenced by amplification, deletion and translocation. Identification of disease genes within these regions is a multi-step, labor intensive process. An approach to rapidly link gene sequence in a candidate interval with expressed proteins in the target tumor would facilitate identification of translocation and amplification associated genes, particularly useful in solid tumor cancer. In cancer patients, autoantibodies against tumor antigens are a common event that can be exploited to identify genes. This proposal presents a novel approach, "epitope trapping", that utilizes the power of diversity and selection from combinatorial phage display libraries to rapidly link DNA sequence in defined regions of the genome with overexpressed and immunogenic proteins in malignancy. In this approach epitope phage display libraries are constructed using sequences from the region of genomic translocation or amplification and are screened against autoantibody containing serum from cancer patients. A "trapped" phage contains a DNA sequence corresponding to a coding (exon) region of the displayed peptide (epitope). A major windfall of this technique is rapid identification of both gene sequence and epitope-specific markers that may provide powerful reagents as serum biomarkers. The specific aims will establish proof-of-principle to epitope trap DNA sequences from the t(15;17) translocation of acute promyelocytic leukemia and the 17q21 region of erb-b2 amplification. Immunodominant epitopes will be identified and screened against multiple cancer patient sera for utility as biomarkers. This proposal will allow the PI to develop his physician-scientist career by applying a series of unique and powerful tools to conduct translational research to impact development of biomarkers of cancer genes, disease progression and therapy.